Currently, the most widely utilized deposition technique for a variety of metallic films in Very Large Scale Integration (VSLI) fabrication is sputtering. Sputtering is a physical vapor deposition (PVD) mechanism whereby material is removed, as atoms or molecules, from a solid target by energetic ion bombardment and deposited as atomic layers on a substrate. PVD involves ionization of argon gas at a low pressure through the use of an electric field. Positive argon ions are accelerated into a negatively charged plate called the target. When these ions strike the target plate, atoms of the target material are sputtered off and then recondense on ambient surfaces to form thin films. Other basic modes of sputtering includes DC magnetron, RF magnetron, RF diode and RF triode. The DC magnetron mode of sputtering has been a popular method of depositing aluminum since the late 1970's. However, by using RF power instead of DC, target materials that are not conductors may be deposited. RF energy is applied to the back surface of the target and is capacitively coupled to the front surface. The difference in mobility between the electrons and ions in the RF formed plasma, causes the surface of the insulating target to acquire a net negative charge of several thousand volts. Positively charged argon ions in the plasma are attracted to the surface of the target causing sputtering to occur.
During the sputtering process, not only is the metallic material deposited on the substrate, but also, on shields used in the sputtering tool to protect the chamber surfaces from the sauttered material. The metallic materials adhere to the shields and over a period of time will "flake" off the shields onto the wafers that are present in the sputtering tool and contaminate the wafers. Of course, as is well known, it is extremely important that the wafer remain as contaminant-free as possible to assure high quality and reliability of the semiconductor devices that are typically formed on the wafer. To minimize the contamination from the shields, the shields are periodically removed and cleaned, in accordance with the manufacturer's specifications.
The cleaning process includes a step to roughen the shield's surfaces to approximately 80 to 120 .mu.inches, typical manufacturers' specification for this type of shields. For certain materials, e.g., titanium nitride (TiN), however, a rougher shield, i.e., greater than 200 .mu.inches, is more desirable because TiN adheres more readily to a rougher surface. Currently, available cleaning processes will not achieve the level of roughness desired primarily because of the thickness of the shields, which is typically 0.040 inches. To achieve the level of roughness desired, the relatively thin shields will be damaged by the roughing process.